Method of forming a woven fiber structure using a tackifier composition

ABSTRACT

A method of forming a woven fiber structure for a molding process to produce a ceramic matrix composite, includes depositing a tackifier composition having a carrier solvent, a resin material, and an inorganic filler onto at least a portion of a woven fiber structure; drying the tackifier composition on woven fiber structure to remove at least a portion of the carrier solvent from the tackifier composition; and forming the dried woven fiber structure into a preform.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. patent application Ser. No.12/625,936, filed on Nov. 25, 2009.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The U.S. Government may have certain rights in this disclosure, asprovided for under Contract No. N00019-02-C-3003 awarded by the UnitedStates Navy.

BACKGROUND

This disclosure relates to woven fiber structures for molding processesthat may be used to produce ceramic matrix composites.

Tackifiers are known and used in polymer matrix composites to hold afiber structure in a desired shape. As an example, a fiber structurealone may be pliable but does not readily hold the shape to which it isdeformed. The tackifier is therefore applied to the fiber structure tofacilitate holding that shape while permitting the structure to bedeformed into the desired shape. The tackifier may also be used toattach woven fiber sheets together and facilitate handling of the fiberstructure.

SUMMARY

According to an exemplary aspect of the present disclosure, a method offorming a woven fiber structure for a molding process to produce aceramic matrix composite includes depositing a tackifier compositionhaving a carrier solvent, a resin material, and an inorganic filler ontoat least a portion of a woven fiber structure; drying the tackifiercomposition on woven fiber structure to remove at least a portion of thecarrier solvent from the tackifier composition; and forming the driedwoven fiber structure into a preform.

A further non-limiting example includes depositing a preceramic polymerinto the preform to form a green state composite.

A further non-limiting example of any of the foregoing examples includespyrolyzing the preceramic polymer to form a ceramic matrix.

A further non-limiting example of any of the foregoing examples includesheating the green state composite to pyrolyze the preceramic polymer andremove the resin material from the tackifier composition, with theinorganic filler remaining in the green state composite.

In a further non-limiting example of any of the foregoing examples, theinorganic filler is a ceramic material.

In a further non-limiting example of any of the foregoing examples, theceramic material is selected from a group consisting of carbides,nitrides, oxides, and combinations thereof.

In a further non-limiting example of any of the foregoing examples, theceramic material is silicon nitride.

In a further non-limiting example of any of the foregoing examples, theresin material includes an epoxy resin.

In a further non-limiting example of any of the foregoing examples, theresin material includes at least two different types of epoxy resins.

In a further non-limiting example of any of the foregoing examples, oneof the epoxy resins has an epoxy equivalent weight of 175-200 g/eq andanother of the epoxy resins has an epoxy equivalent weight of 500-575g/eq.

In a further non-limiting example of any of the foregoing examples, theinorganic filler is a ceramic material and the resin material includesan epoxy resin.

In a further non-limiting example of any of the foregoing examples, thetackifier composition includes 22-42 wt. % of the resin material, 1-30wt. % of the inorganic filler, and the remainder being the carriersolvent.

In a further non-limiting example of any of the foregoing examples, thetackifier composition includes 27-37 wt. % of the resin material, 18-28wt. % of the inorganic filler, and the remainder being the carriersolvent.

In a further non-limiting example of any of the foregoing examples, thetackifier composition includes 30-34 wt. % of the resin material, 21-25wt. % of the inorganic filler, and the remainder being the carriersolvent.

In a further non-limiting example of any of the foregoing examples, thewoven fiber structure has ceramic fibers.

In a further non-limiting example of any of the foregoing examples, theceramic fibers are silicon carbide.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example tackifier composition.

FIG. 2 illustrates an example method of forming a woven fiber structureusing a disclosed tackifier composition.

FIG. 3 illustrates an example woven fiber structure using a disclosedtackifier composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically illustrates an example of tackifier composition 20that may be used in a molding process to produce a ceramic matrixcomposite (“CMC”). As will be described, the disclosed tackifiercomposition 20 is designed to be physically and chemically compatiblewith the ceramic materials and ceramic processing used to form all typesof CMC articles. Ceramic materials are often processed at much highertemperatures than polymer matrix composites and are also subject toshrinkage during thermal processing of the ceramic material. Tackifiersused in polymeric composite systems with lower processing temperaturesmay thermally degrade under the high temperatures used for ceramicprocessing and thereby exacerbate effects from shrinkage and/or produceresidual degradation byproducts that negatively affect the properties ofthe CMC. The disclosed tackifier composition 20 is designed tofacilitate mitigating such concerns and is universally compatible withall different types of CMC articles.

In the illustrated example, the tackifier composition 20 includes thecomponents of a carrier solvent 22, a resin material 24, and aninorganic filler 26. The components 22, 24, and 26 may be mixed togetherin predetermined amounts to form the tackifier composition 20. In someexamples, the tackifier composition 20 may include only the givencomponents along with impurities that do not materially affect the tackproperties. The tack properties may refer generally to the ability ofthe tackifier composition 20 to facilitate forming a fiber structureinto a preform, ability to bond fiber structures together, and/orability to enhance handling characteristics of a fiber structure.

The carrier solvent 22 is a liquid that facilitates depositing thetackifier composition 20 onto a woven fiber structure, as will bedescribed later in this disclosure. As an example, the carrier solvent22 may be an organic solvent, such as acetone. Other types of organicsolvents, such as polar or non-polar solvents, may alternatively be useddepending upon the type of resin material 24, for instance.

The resin material 24 may be selected to have desirable tack propertiesthat facilitate forming and holding a woven fiber structure in apreform, facilitate bonding fiber structures together, and/or enhancehandling characteristics of a fiber structure. As an example, the resinmaterial 24 may be an epoxy resin, which provides better tack propertiesthan preceramic polymers that may be used to form the CMC. Thus, unlikepolymer matrix composites that utilize tackifiers that are chemicallysimilar to the polymer matrix, the resin of the tackifier composition 20may be chemically and physically different than a preceramic polymerused to form the matrix. Additionally, the epoxy material can be cleanlyremoved in a later ceramic processing heating step to leave little or noresidue that might otherwise affect the physical, chemical, mechanical,or electrical characteristics of the final CMC. In this regard, portionsof the tackifier composition 20 are sacrificial in that the tackifiercomposition 20 is used with the woven fiber structure to provide tackproperties but is then at least partially removed after serving thisfunction.

The resin material 24 may include a single type of resin or a blend oftwo or more different types of resins. For instance, a first epoxy resinmay have weak tack properties and a second epoxy resin in the blend mayhave strong tack properties such that a blend of the two different epoxyresins provides a desirable composite tack property. For instance, oneof the resins may be D.E.R. 331 (Dow Chemical Company) and the otherresin may be Epon 1001F (Shell Oil Company). The epoxy resins may befurther characterized by an epoxy equivalent weight or other property.In this regard, one of the epoxy materials may have an epoxy equivalentweight of 175-200 g/eq and another epoxy material used in the blend mayhave an epoxy equivalent weight of 500-575 g/eq. Given this description,one of ordinary in the art will recognize other types or blends of epoxyresins, or even other types of resins that may be used in the tackifiercomposition 20.

The inorganic filler 26 of the tackifier composition 20 may be a ceramicmaterial, such as a carbide, nitride, oxide, or combination thereof.That is, the ceramic material may be a blend of several different typesof ceramic powders or a single type of material that includes nitrogen,carbon, and/or oxygen. In one example, the ceramic material may besilicon nitride (Si₃N₄) powder. As will be described below, theinorganic filler 26 facilitates mitigating effects from shrinkage duringthe processing of the CMC.

The components of the tackifier composition 20 may be provided inpredetermined amounts. In one example, the tackifier composition 20includes 22-42 wt. % of the resin material 24, 1-30 wt. % of theinorganic filler 26, and the remainder being the carrier solvent 22. Infurther examples, the tackifier composition 20 may include 27-37 wt. %of the resin material 24, 18-28 wt. % of the inorganic filler 26, andthe remainder being the carrier solvent 22. In a further example, thetackifier composition 20 may include 30-34 wt. % of the resin material24, 21-25 wt. % of the inorganic filler 26, and the remainder of thecarrier solvent 22. That is, the amounts of the components may beadjusted within the given example ranges to provide the tackifiercomposition 20 with desirable properties with regard to tack, viscosity,and ability to be cleanly removed during ceramic processing.

FIG. 2 illustrates selected steps of an example method 40 of forming awoven fiber structure for a molding process to produce a CMC using theabove-described tackifier composition 20. In this example, the method 40includes a deposition step 42, a drying step 44, and a forming step 46.The deposition step 42 may include depositing the tackifier composition20 onto at least a portion of the woven fiber structure, which may be atwo-dimensional broadcloth fiber structure, three dimensional fiberstructure, or combination thereof. As an example, the tackifiercomposition 20 may be applied to surfaces of individual sheets ofbroadcloth, such as sheets of eight harness satin weave. The woven fiberstructure is therefore generally not limited to any particular type ofstructure. Additionally, the tackifier composition 20 is universallyapplicable to different types of CMC articles and the fibers of thewoven fiber structure may therefore be any type of ceramic materialdesired in the final composition of the CMC. In one example, the fibersmay be silicon carbide (SiC), such as cg-Nicalon (Nippon Carbon CompanyLimited). However, in other examples, the fibers may be other types ofcarbides, nitrides, oxides, or combinations thereof.

The tackifier composition 20 may be deposited onto the surfaces of thewoven fiber structure (e.g., surfaces of an individual sheet). In thisregard, the tackifier composition 20 may be applied only to the surfacesor surface of a sheet or fiber structure and need not necessarily coverall surfaces of the fibers. As an example, the tackifier composition 20may be spray-deposited onto the woven fiber structure, melt-infused ontothe woven fiber structure in a pressure/heat transfer process, orcombinations of these techniques. Moreover, the amounts of thecomponents in the tackifier composition 20 may be adjusted to bettersuit a particular desired deposition technique, such as to achieve adesired viscosity.

After deposition, the tackifier composition 20 on the woven fiberstructure or sheet is dried in the drying step 44 to remove asubstantial portion of the carrier solvent 22. For instance, the carriersolvent 22 may evaporate and/or the woven fiber structure or sheet maybe subjected to heat and/or reduced pressure to remove a substantialportion of, or all of, the carrier solvent 22 from the tackifiercomposition 20 by evaporation. In the case of a sheet, the sheet maythen be cut into predefined shapes or plies. For example, the sheet maybe held flat and cut into patterns. The handling characteristics of thetackifier composition 20 facilitate maintaining the shape and edgeintegrity of the patterns during cutting and handling.

The dried woven fiber structure or cutout patterns may then be formed inthe forming step 46 into a preform. For instance, the cutout patternsmay be stacked, such as on a layup mandel having a shape correspondingto the geometry of the part. During stacking, the tackifier composition20 enables the cutout patterns to stick together as the preform is builtup from the cutout patterns. Heat and pressure may be applied during theforming or stacking to compact the preform, form a desired shape, and/orto partially polymerize the resin material 24 in the preform.Alternatively, the forming of the fiber preform may be conducted atambient temperatures with limited or no polymerization. In this regard,the resin material 24 may be free of any catalyzing agent if nopolymerization is desired or may include a low level of catalyzing agentif partial polymerization is desired.

Three-dimensional woven structures may also be incorporated with thewoven fiber structure or cutout patterns. For instance, the tackifiercomposition 20 may also be applied to the surfaces of thethree-dimensional woven structure that mate with the woven fiberstructure or cutout patterns to facilitate holing the structurestogether.

After the formation of the woven fiber structure into the desired shape,the preform may be subjected to a molding process for forming the CMC.For instance, the molding process may be a resin transfer moldingprocess in which a material, such as a preceramic polymer, isinfiltrated into the spaces between the fibers of the fiber preform. Thepreceramic polymer and fiber preform thereby form a green statecomposite. The green state composite may be then subjected to heatingsteps to polymerize and pyrolyze the preceramic polymer to form the CMC.Multiple cycles of infusing the preceramic polymer and pyrolyzing thepreceramic polymer may be used to achieve a fully dense matrix.

As an example, the preceramic polymer may be a polysilazane for forminga silicon-containing ceramic matrix, such as amorphous siliconcarbonitride (SiNC) using S-200 (COI Ceramics, Inc.). It is to beunderstood that the tackifier composition 20 is universally compatibleand may therefore be used with other types of preceramic polymers.

The heating of the green state composite to form the CMC also removesthe resin material 24. For instance, the processing of ceramic materialsresults in shrinkage as the preceramic polymer pyrolyzes and densifiesinto ceramic material. Shrinkage of preceramic polymers can beapproximately 40 vol %. To reduce effects of shrinkage, such as atendency of the composite to crumble or fracture from lack of mechanicalstrength, the tackifier composition 20 includes the inorganic filler 26.The inorganic filler 26 does not thermally decompose during the heatingand thereby remains as a stable reinforcing agent to increase themechanical strength of the composite during processing. Thus, theinorganic filler 26 facilitates processing of the CMC whereas tackifierswithout inorganic filler would not provide any reinforcing effect.

FIG. 3 illustrates an example cross-section of a dried woven fiberstructure 60 after the drying step 44 of the method 40. In this example,the dried woven fiber structure 60 includes a fiber structure 62, whichmay be a sheet or sheets of woven fiber, such as eight harness satinweave of cg-Nicalon. The dried woven fiber structure is coated on one orboth sides with dried tackifier composition 20′. The dried tackifiercomposition 20′ may be substantially free of any of the carrier solvent22 after the drying step 44. Thus, all that remains of the originaltackifier composition 20 are particles of the inorganic filler 26dispersed within the resin material 24. In some examples, the driedwoven fiber structure 60 may be pre-prepared for a later molding processto fabricate the CMC.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. A method of forming a woven fiber structure for amolding process to produce a ceramic matrix composite, comprising: a)depositing a tackifier composition having a carrier solvent, a resinmaterial, and an inorganic filler onto at least a portion of a wovenfiber structure, wherein the resin material includes at least twodifferent types of epoxy resins, and one of the epoxy resins has anepoxy equivalent weight of 175-200 g/eq and another of the epoxy resinshas an epoxy equivalent weight of 500-575 g/eq; b) drying the tackifiercomposition on woven fiber structure to remove at least a portion of thecarrier solvent from the tackifier composition; and c) forming the driedwoven fiber structure into a preform.
 2. The method as recited in claim1, further including depositing a preceramic polymer into the preform toform a green state composite.
 3. The method as recited in claim 2,further including pyrolyzing the preceramic polymer to form a ceramicmatrix.
 4. The method as recited in claim 2, further including heatingthe green state composite to pyrolyze the preceramic polymer and removethe resin material from the tackifier composition, with the inorganicfiller remaining in the green state composite.
 5. The method as recitedin claim 1, wherein the inorganic filler is a ceramic material.
 6. Themethod as recited in claim 5, wherein the ceramic material is selectedfrom a group consisting of carbides, nitrides, oxides, and combinationsthereof.
 7. The method as recited in claim 5, wherein the ceramicmaterial is silicon nitride.
 8. The method as recited in claim 1,wherein the inorganic filler is a ceramic material and the resinmaterial includes an epoxy resin.
 9. The method as recited in claim 1,wherein the tackifier composition includes 22-42 wt. % of the resinmaterial, 1-30 wt. % of the inorganic filler, and the remainder beingthe carrier solvent.
 10. The method as recited in claim 1, wherein thetackifier composition includes 27-37 wt. % of the resin material, 18-28wt. % of the inorganic filler, and the remainder being the carriersolvent.
 11. The method as recited in claim 1, wherein the tackifiercomposition includes 30-34 wt. % of the resin material, 21-25 wt. % ofthe inorganic filler, and the remainder being the carrier solvent. 12.The method as recited in claim 1, wherein the woven fiber structure hasceramic fibers.
 13. The method as recited in claim 12, wherein theceramic fibers are silicon carbide.